The field of this invention is that of the use of line-projection procedures to make contact free 3 dimensional measurements of objects. Line-projection procedures are known in the art and have been implemented in optical 3D-measuring technology for several years. These line-projection procedures are also called “structured light”. There are procedures using a projection system with fixed line distance and projection systems with variable line distance. Procedures with variable line distance are advantageous to enable coding of the projected image to assist in surface measurement. These line-projection procedures are also called “coded structured light”. Somewhat more advanced procedures referred to as phase-code procedures are also used.
Many techniques for 3D measurement using structured light projection for measurement of stationary objects have been developed. All methods of this type project an intensity pattern on the test object and record the deformation of the pattern induced by the shape of the object as observed from an angle offset from the illumination direction. The object shape may then be derived from the observed pattern. One or more projection/record cycles are required depending upon the measurement technique. Multiple projection/record cycles are commonly required by measurement techniques employing projection patterns with varying phase or other variation to produce high quality measurements. Another common method is use of multiple projection cycles to produce varying intensity levels. The elapsed time for each projection/record cycle limits the application of the technique to objects stationary during the projection/record cycles.
The measuring results and information attainable with the line-projection procedure, in connection with the optical and microscopic systems used, largely depend on the quality of the projected lines. For numerous technical measuring applications it is necessary to generate not only bicolor modulated lines (black/white structures) with rectangular intensity structures, but also gray scale phase-modulated lines with a defined sinusoidal intensity structure to be projected onto the object during the same measuring cycle.
Frankowski (U.S. Pat. No. 6,611,343) presented an approach to provide the defined intensity patterns needed through use of a micro-mirror projector. Through creation and projection of the line intensities with a micro-mirror projector, where a large number of individually computer controlled micro-mirror sections are arranged on a carrier, defined intensity structures can be created in strip and line patterns commonly used in 3D-measuring technology, but also in sinusoidal modulation within an extremely short time frame within the recording cycle. It is also possible to create geometric intensity structures adapted to the 3D-profile of the object, such as circles, dots, cross shapes, ellipses, rectangles, and others. Their interference with the object geometry ensures a highly precise computerized recording of the 3D-profile of the object, the intensity structures created with this invention having a high contrast, resulting in a definite increase in measuring precision, performance, and information attainable with the 3D-measuring technology. In addition laser speckle and statistical noise patterns can be generated using this approach.
The elapsed time for each projection/record cycle limits the application of the technique to objects stationary during the projection/record cycles. There are a growing number of applications however where the object to be measured is not stationary. There is a need then for using these defined intensity projection techniques for objects that in operation exhibit periodic motion such as rotation or oscillation. Periodic meaning in this case that the objects being measured are moving in repeated cycles.